1. Field of the Invention
The present invention relates to flat panel displays which can be operated at a low voltage on the basis of vacuum tunneling, thereby realizing a long life and uniformity.
2. Description of the Prior Art
The most widely popularized display in the world is the cathode ray tube (CRT). Recently, however, the increasing desire to represent images more largely and sharply has led attention to be paid to flat panel displays. Examples of conventional flat panel displays include liquid-crystal displays (LCDs), electroluminescent displays (ELDs), field-emission displays (FEDs), plasma display panels (PDPs), vacuum fluorescent displays (VFDs), flat panel CRTs and light emitting diodes (LEDs).
Of these flat panel displays, LCDs are the most prevailing, and FEDs are a strong competitor in the flat panel display market currently dominated by LCD manufacturers. Typically, an LCD consists of cell structures, in each of which a phosphor-coated front member is combined with a cathode emitter-equipped backing member with a predetermined vacuum spacing therebetween. If a potential ranging from hundreds to tens of thousands of volts is applied across the front member and the backing member, electrons are emitted from the electron emitter and collide against the phosphor coating to make luminescence.
Referring to FIG. 1, there is a cell structure for a pixel of a conventional FED employing a microtip type vacuum transistor. As shown in this figure, this conventional FED cell structure is composed of a front panel structure 1 and a backing panel structure 2, the front panel structure 1 comprising a front panel 3 underlaid with a transparent anode 4 whose bottom is coated with a phosphor 5, the backing panel structure 2 comprising a backing panel 6 on which a cathode 9 with a tip t, an insulating layer 8 and a gate electrode 7 are sequentially formed.
When a strong electric field is applied between the cathode 9 and the gate 7, electrons are quantum-mechanically emitted from the metal surface of the cathode tip t, then accelerated by the high voltage applied to the transparent anode 4, and finally collide against the phosphor coating 5 on the anode 4 to emit light.
To accomplish proper emission of free electrons from a metal surface in a vacuum, an electric field of 0.5 V/or higher is required. For this, the diameter of the gate which surrounds the electron emission spot centering around the metal cathode tip must be much smaller than 1 xcexcm. The production of such a microtip as in the FED must be based on a photolithography process with which a resolution of 1 xcexcm or less can be attained and maintained. Where the semiconductor production techniques in current use, which have been significantly advanced, and the production techniques for other displays are combined, the microtip can be manufactured, but in a small scale. Much time is still needed for establishing a complete process by which the microtip can be mass produced.
Apart from the spacing between the electrodes and the formation of the sharp-pointed electron emitter, a material which is stable and has a low work function is required for a successful FED. Such a stable and low work function material allows a low operation voltage for the display. Many research reports on microtips using such metals as molybdenum (Mo) and tungsten (W) have been published. Molybdenum are tungsten show an advantage of being mechanically stable, but are disadvantageous in that they have a large work function and show a limitation in reducing the curvature radius at the end of the tip. Thus, the FEDs employing the metals are still high in operation voltage.
Recently, microtips have been developed in various aspects, including surface treatment of microtips to reduce the work function and employment of low work function materials such as diamond like materials.
However, the FEDs using the microtips under current research in current suffer from disadvantages in that:
First, the tips are damaged by ion sputtering during operation.
Second, the microtips are difficult to produce. The electron emission efficiency in an FED has a direct influence on its luminance and resolution. So, the structure and construction process of the micro tip, the structural optimization associated with the shapes and spacings of electrodes, and the selection of electron emitting materials, which all play critical roles in determining the electron emission efficiency, are very important. However, technical difficulties still remain on the current construction processes of the microtip. The spacing between electrodes and production methods thereof also provide another technical difficulty.
Third, it is difficult to accomplish spacial uniformity. The microtips do not easily attain uniformity even by the same process procedure. Since each pixel consists of a plurality of unit cells, the presence of a few bad cells does not critically affect the function of the cell. However, if the microtips are nonuniform among the pixels, the image realized on the display is not stable.
Fourth, flickering takes place.
Fifth, arc discharge occurs owing to the high electric field between the gate and the cathode tip, breaking the gate and/or the cathode tip. In practice, during processing or operating, the vacuum degree may be decreased. In addition, because the spacing between the electrodes is very narrow, if impurities such as heterogeneous metal atoms are deposited between the electrodes, arc discharge easily arises.
Finally, arc discharge may also occur between the gate and the anode even though they are apart from each other at a relatively long distance. Despite this condition, the high voltage which is applied to the anode to accelerate the electrons emitted from the microtips, may cause arc discharge.
Much advance has been made on the above mentioned technical subjects. However, the problems are attributed fundamentally to the presence of the microtips.
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a novel flat panel field emitter display, which has a planar unit cell structure and thus, allows a high degree of integration.
It is another object of the present invention to provide novel flat panel field emitter display, which is able to realize images of high definition and fast response, and represent all natural colors with a high resolution.
As a result of the intensive and thorough research repeated by the present inventors, a novel flat panel field emitter display which meets the above conditions, was developed and named xe2x80x9cKAIST Field Emitter Displayxe2x80x9d (hereinafter referred to as xe2x80x9cKFEDxe2x80x9d).
In accordance with an aspect of the present invention, there is provided a double panel type flat field emitter display, consisting of a plurality of unit cells, each cell comprising: a front panel structure in which an anode is formed on a transparent front panel and coated with a phosphor; and a backing panel structure in which a cathode and a gate are formed on and beneath a channel insulator underlaid by a backing panel, the front panel structure being joined to the backing panel structure in a vacuum condition in such a way that the phosphor faces toward the cathode, wherein a low voltage is applied between the gate and the cathode to emit electrons from a spot at which the fringe of the cathode is in contact with the channel insulator, to the vacuum channel, and a high voltage is applied to the anode to accelerate the emitted electrons and finally to collide them against the phosphor to luminesce, said emitted electrons being controlled in number by the voltage between the gate and cathode, said cells being arranged in a pattern to form a pixel which represents information.